The invention relates to a method for pulse width modulated control of a plurality of load elements according a method for pulse width modulated control of a plurality of load elements, the load elements being controlled in time staggered manner with respect to each other.
The control of many electrical loads in a motor vehicle (e.g. lamps, heating coils, . . . ) is effected by means of pulse width modulation (PWM). Here, the power delivered to the load can be regulated or controlled, wherein the losses in control electronics can be kept small by the switch operation.
With the pulse width modulated control of loads in the motor vehicle, however, electromagnetical fields are emitted via the battery and load lines, which might disturb radio reception in the vehicle.
Therefore, for this purpose in different standards (IEC, ISO, CISPR) limiting values have been defined, which reduce impact of the radio receiver in the corresponding spectrums to a tolerable degree.
Suppression of the alternative currents on the lines is usually effected with low-pass filters (LC) in the input lines. Size and also costs of the filters conform with ampacity, required attenuation, quality and cut-off frequency. In motor vehicle control units the PWM is normally generated via timer modules integrated for a plurality of load elements into the microcontroller, all PWM-outputs connecting at the same time and disconnecting at different times depending on the PWM-repetition rate.
The disadvantage of this method is that a very high alternating current is taken from the mains, and, therefore, high demands must be made to the used filters, in particular to the storage condensers.
From EP-A2-0 982 194 a method for controlling electrical consumers in a supply system, for example of a motor vehicle, is known, in which the active state of the electrical consumer is constantly monitored and its control is effected by means of at least one control unit. This method allows for the best possible driving comfort under all operating conditions of the motor vehicle. A classification of all electrical consumers of the system into strategy groups, as well as a definition of control algorithms and priorities for the individual strategy groups, the storage of the classification and of the control algorithms of the strategy groups in a storage is effected. Furthermore, monitoring of all electrical consumers is effected by the control unit and storing of all detected data in the storage, as well as the simultaneous or time staggered control of the electrical consumer by the control unit after having evaluated the switching requirements of superior electrical consumers and release of the control of correspondingly defined algorithms.
Form U.S. Pat. No. 4,176,250 a multiplexer system with pulse width modulation for use in a motor vehicle is known. The system includes a transmitter assembly, which is located in the left front door, which transmits information to the receiver components, which are interconnected by a data line and which are arranged in the passenger doors and under the front seat. The receiver in the right front door is embodied in such manner that information can be delivered to the connected systems. An interference of the individual systems among each other is avoided by priority logistics.
It is the object of the invention to indicate a method of the above-mentioned type, by means of which the interferences can be further reduced.